Breath alcohol measurements have been known per se and are carried out with various different measuring devices and methods. For example, U.S. Pat. No. 6,167,746 B1 shows a measuring device that comprises a measuring tube, to which a pressure sensor and a temperature sensor as well as a gas sampling valve with an electrochemical measuring cell arranged downstream of the valve for the measurement of the breath alcohol concentration are connected one after another in the direction of flow of the gas.
Prior-art breath alcohol measuring devices, e.g., the Alcotest® devices, have been used for some years for the specific monitoring of the breath alcohol concentration of drivers especially during traffic checks.
Breath alcohol measuring devices are also used in combination with so-called “interlock” systems in private motor vehicles to prevent driving under the influence of alcohol. The alcohol test in these applications is not performed under the supervision of authorized persons. It is therefore especially important in these “interlock” systems either to rule out attempts at manipulating with the breath alcohol measurement and/or to have the possibility of detecting such attempts by recording characteristic measured variables, e.g., during the reading of the operating data at an authorized service station. The result of the measurement for the breath alcohol concentration can be manipulated, e.g., by passing the breathing air over a wash bottle or through filter materials, by sending air from an air reservoir into the measuring device or the like.